1. Field of the Invention
The present invention relates to an ultrasound diagnostic apparatus and ultrasound image processing method which estimate the speed of living tissue such as cardiac muscle by using ultrasound waves, and output the local motion information of the tissue by processing the estimated velocity information, thereby providing information effective for medical diagnosis.
2. Description of the Related Art
With regard to living tissue such as cardiac muscle, it is very important for the diagnosis of the tissue to objectively and quantitatively evaluate its function.
Various kinds of quantitative evaluation methods have been tried. A stress echo method using an ultrasound diagnostic apparatus has recently attracted attention. In this method, for example, a subject to be examined is made to jog, and images of the cardiac muscle are taken before and after jogging. These images are then compared with each other to make diagnosis on a region having abnormality.
In this type of examination, it is preferable to avoid diagnosis based on the subjectivity of an examiner by quantifying comparison before and after the application of a stress (load). Various methods have been proposed for this purpose.
For example, a method using a dedicated left ventricular wall motion analysis apparatus is known. An ultrasound diagnostic apparatus which can easily and accurately perform diagnosis by the stress echo method is also disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-285066. In addition, a method which can mainly image how local delay of wall motion occurs for each region is disclosed in Japanese Patent No. 3187008.
In the method using the dedicated left ventricular wall motion analysis apparatus, tracing or the like of an endocardium is required, and complicated operation is required.
Velocity information on a living organ tends to become unstable due to the influences of speckle noise and the like. Acceleration information is further susceptible to the influence of noise. According to the ultrasound diagnostic apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-285066, since such information is compared, it is difficult to obtain a stable result with high reproducibility.
In an ischemic heart disease case, even if a wall motion looks normal before the application of a load, ischemia is induced by the application of the load, and local delay of the wall motion may occur. The method disclosed in Japanese Patent No. 3187008 performs no comparison before and after the application of a load unlike in the stress echo method. For this reason, it is not easy to detect a slight change in the state of local delay described above before and after the application of a load.